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Heavy rainfall alert: Fri 11th - Mon 14th Sept

  • 10-09-2015 5:31pm
    #1
    Registered Users Posts: 14,268 ✭✭✭✭M.T. Cranium


    I was going to post a LEVEL 1 alert but numerical guidance from several global models are indicating potential for 50 or even 60 mm rainfalls between Friday early morning and Saturday mid-day. Despite the recent run of dry weather, that could be enough rain to produce considerable flooding in low-lying and poorly drained areas and especially on roadways.

    The cause of this heavy rainfall is a very slow moving low pressure trough oriented NNW-SSE already making landfall in west Munster then coastal Mayo this evening. Numerical weather prediction is of course not a perfect science but be forewarned, the GFS model indicates 40-60 mm rainfalls possible in parts of central and southeast Connacht and western to central Munster, and amounts of 30-50 mm in most other counties. The GEM model has output that I recognize as top end for their model, whatever their objective number crunch shows, the intensity alone has me concerned given the very slow pace of this system.

    It will rain steadily and sometimes very heavily (thundery bursts are possible) for at least 12 to 18 hours once the rain begins in any one location and possibly for 24 hours straight. So the flood potential comes more from that duration than any one hour or two within the system. I am expecting to see reports of 7-12 mm an hour rainfalls and perhaps several consecutive ones.

    While almost anywhere in the road network and in towns and cities (in favoured locations) could see flooding at some point, I think that Cork and possibly some towns in Roscommon, east Galway and southeast Mayo would be somewhat more likely to see serious urban flooding problems (underpasses filling up with 3-5 feet of water not out of the question, for example). There won't be much wind as this low is rather weak in terms of pressure gradient, but with new moon approaching on the 13th, tides will be increasing and this could interact with the runoff near the south coast to exacerbate flooding problems.

    Will end this thread after a discussion with a map showing actual total rainfalls including those of Boards members, be sure to post some totals (Friday-Saturday) if you can in either this thread or the observations thread.

    As this is likely to come up, expect the rain to end Friday night in many places but mid-day Saturday in Dublin-Kildare and Saturday afternoon north of there. The system will tend to "pivot" during Friday night which is why southeast Connacht and far west Leinster would be perhaps subject to higher totals. The smallest totals might be expected in northwest Donegal and southeast Wexford perhaps (25 mm might be the minimum).

    Please note that the thread title was upgraded at 1430h Friday to reflect two concerns -- the rainfall event Friday-Saturday will be followed in parts of the west by further heavy rain Sunday-Monday, and total rainfalls over that period (counting what has already fallen to 1430h Friday) may exceed 100 mm over large portions of Kerry, Cork, west Limerick, Clare, Galway and Mayo. This introduces a LEVEL 3 "take action" alert status for a few, still considering that these totals are over 96 hours the runoff into other more populated areas such as Cork city may stay inside the LEVEL 2 criterion but stay in close touch with your local flood authorities for updates through Monday in parts of west Munster and Connacht.

    Note: As of 0300h Saturday, most of the rainfall from "round one" of this two-part rainfall extravaganza has moved to the east coast and parts of Ulster where it should gradually wind down later on this morning. A second burst of moderate or possibly heavy rainfall will spread in from the south on Sunday and may peak on Monday in western Connacht (again). This second round is not expected to be as heavy although 30-50 mm could fall in some of the same places that saw 75-125 mm on Friday. Some parts of the east and north are not expected to see much more than 10 mm from round two. The southeast may see 20 mm.


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Comments

  • Closed Accounts Posts: 40,061 ✭✭✭✭Harry Palmr


    Well the place is starting in get a bit dusty.


  • Registered Users Posts: 11,134 ✭✭✭✭maquiladora


    This may be overdoing it a tad, but the 12Z WRF NMM is showing 150mm over high ground. The Met Eireann criteria for a red warning is +70mm.

    09YlDnW.png


  • Registered Users Posts: 1,491 ✭✭✭Reckless Abandonment


    Euro4 is up into the hundred plus mark too


  • Registered Users Posts: 14,268 ✭✭✭✭M.T. Cranium


    Readers should note that the map is for mid-event in central regions and somewhat before peak potential in Leinster.

    This would all suggest extreme caution in driving in hilly areas Friday night in particular when you can't see as well ahead of you, if those rainfall totals were to verify on higher ground, some culverts could be washed out and minor landslides or certainly mudslides would be possible, bad enough if you can see them ahead of you, worse if you're rattling along at 70 km/hr and run into them.

    Same goes for flooding of darkened roadways which you could expect to encounter near small stream bridges and lower portions in areas with variable elevation.

    It's a big change in the weather too, that often catches people unawares, not like it has been raining off and on for weeks.


  • Registered Users Posts: 6,235 ✭✭✭Oneiric 3


    Where the ECM 12z has the heaviest rain tomorrow at 18z. Transfers east during the evening.

    361877.PNG

    GFS 12z has over 70 mm falling in my area over a 24 hour period, ECM has less than half of that. My rain gauge dusted off to test which model will be closer the mark.

    New Moon



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  • Registered Users Posts: 11,134 ✭✭✭✭maquiladora


    12Z ICON also showing 100mm in places by Saturday morning.

    VB4qnEW.gif


  • Moderators, Science, Health & Environment Moderators Posts: 11,746 Mod ✭✭✭✭Meteorite58


    Rain started her near Tralee at 18.00, 7mm so far with some heavy bursts. Raining lighter atm

    Must say didn't expect anything like what is being forecast.

    Feeling mild at 15.3C


  • Registered Users Posts: 6,235 ✭✭✭Oneiric 3


    12Z ICON also showing 100mm in places by Saturday morning.

    YR 12z showing about half that but within the same overall area.

    361879.PNG

    Would not be surprised if these highest totals transferred a little more east in later runs.

    New Moon



  • Banned (with Prison Access) Posts: 210 ✭✭Tompatrick


    I am flying into Shannon tomorrow. Will this be problematic ?


  • Registered Users Posts: 10,017 ✭✭✭✭Oscar Bravo


    Tom, there shouldnt be any problems, CATII ILS approaches tomorrow at times, just a horrible wet day
    TAF EINN 101700Z 1018/1118 14018KT 9999 SCT015 BKN030
    BECMG 1021/1023 -RA BKN013
    TEMPO 1101/1118 4000 RA SCT005 BKN008 PROB40
    TEMPO 1103/1117 2000 +RA BKN005
    BECMG 1108/1110 17008KT
    BECMG 1115/1117 31014KT= A mucky day


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  • Moderators, Science, Health & Environment Moderators Posts: 11,746 Mod ✭✭✭✭Meteorite58


    Tralee: Heavy rain again, 10mm ( checked against the manual gauge )


  • Registered Users Posts: 10,017 ✭✭✭✭Oscar Bravo


    Getting it's act together up along the coast


  • Registered Users Posts: 14,268 ✭✭✭✭M.T. Cranium


    Here's my attempt at a numerical prediction:

    361895.jpg


  • Moderators, Science, Health & Environment Moderators Posts: 11,746 Mod ✭✭✭✭Meteorite58


    Very heavy rain here near Tralee
    Rain Rate 25mm per Hour

    15mm and counting


  • Registered Users Posts: 3,027 ✭✭✭redsteveireland


    I love these events that sneak up when you are not paying attention. Looks like fun here tomorrow.

    Some sporting events likely to be affected Saturday morning?


  • Registered Users Posts: 3,027 ✭✭✭redsteveireland


    Oneiric 3 wrote: »
    Where the ECM 12z has the heaviest rain tomorrow at 18z. Transfers east during the evening.

    361877.PNG

    GFS 12z has over 70 mm falling in my area over a 24 hour period, ECM has less than half of that. My rain gauge dusted off to test which model will be closer the mark.

    That kind of turquoise line is 70mm is it?


  • Registered Users Posts: 5,803 ✭✭✭Chris_5339762


    Our hike is cancelled for Saturday morning thanks to the advice of this thread! Not wanting to do a daft rampage in the pouring rain.


  • Registered Users Posts: 14,237 ✭✭✭✭leahyl


    Any idea of the speed at which this front is travelling? I'm planning on going out for dinner in Cork City tomorrow evening at 7.30 - will the rain have eased a bit here at that stage?


  • Registered Users Posts: 10,017 ✭✭✭✭Oscar Bravo


    2222 update from met eireann

    10 September 2015 22:22

    Today
    Rain will be widespread across Connacht and most parts of Munster overnight, with heavy falls in the west and southwest and some spot flooding. But it will remain misty and mostly dry elsewhere, with just some patchy drizzle and rain by morning. Lowest temperatures 11 to 14 C., in freshening southeasterly winds.




    Tomorrow

    Patchy rain at times over east Leinster and much of Ulster in the morning. But very wet elsewhere, with some heavy and locally thundery falls of rain and some flooding. Breezy with top temperatures 14 to 17 C., Fresh and gusty southeasterly winds, will veer northwesterly on west and southwest coasts in the afternoon and evening.

    Outlook

    FRIDAY NIGHT: Widespread heavy rainfall affecting eastern and northern areas, with further spot flooding, but the rain will clear southwestern areas overnight. Lowest temperatures of 6 to 11 degrees, coolest over Munster in the clearance later. Winds will be mostly moderate westerly, fresher near coastal areas.

    SATURDAY: A wet start in the north and northeast but the rain will gradually clear from the southwest. Over the southern half of the country the day will be mostly dry with some sunny spells and just a few showers feeding in from the Atlantic. Cooler than recent days with highest temperatures 14 to 16 degrees, in light to moderate westerly winds.

    SUNDAY: Rather cloudy with rain spreading from the south, but mostly dry at first in northern areas in light easterly breezes becoming moderate to fresh southerly later. Highest temperatures of 13 to 15 or 16 degrees, coolest across southern counties.

    MONDAY: A wet start in many areas with widespread rain, only clearing slowly eastwards later in the day. Still cool, with highs of 12 to 15 degrees, with winds northwesterly moderate to fresh at first but becoming light to moderate westerly later.

    NEXT WEEK: Unsettled, spells of wet and windy weather, but mild at times too.


  • Registered Users Posts: 11,134 ✭✭✭✭maquiladora


    leahyl wrote: »
    Any idea of the speed at which this front is travelling? I'm planning on going out for dinner in Cork City tomorrow evening at 7.30 - will the rain have eased a bit here at that stage?

    Could well be at it's heaviest around Cork at that time.


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  • Registered Users Posts: 11,134 ✭✭✭✭maquiladora


    Very heavy rain here near Tralee
    Rain Rate 25mm per Hour

    15mm and counting

    If this is right, the heaviest rain won't be reaching you until after 6am tomorrow.

    http://www.met.ie/forecasts/short-range.asp


  • Registered Users Posts: 2,575 ✭✭✭monkeysnapper


    Talk about a stupid day to sell my car . I'm walking 30 mins to work for next few weeks starting tomorrow . Doh!!!


  • Registered Users Posts: 14,237 ✭✭✭✭leahyl


    Could well be at it's heaviest around Cork at that time.

    That's just fabulous thank you.... :-D


  • Registered Users Posts: 6,827 ✭✭✭pauldry


    I remember June either 2012 or 2013 it was the 8th I think and there was 78mm of rainfail in Sligo over 2 days with a se wind and slow moving front.

    Saw BBC forecast 50mm very possible tomorrow n dry september with 9% rain becomes washout with 75% in first 11 days


  • Moderators, Science, Health & Environment Moderators Posts: 11,746 Mod ✭✭✭✭Meteorite58


    24mm here since 18.00 ( gone light atm ) Going to be some totals by sat morning.

    Wind picking up avg 23 kph SSE, gust 45.1 kph

    Mild at 15C


  • Registered Users Posts: 10,017 ✭✭✭✭Oscar Bravo


    Its coming up to 1155 so lets head over to met eireann for the general and sea area forecast on Rte radio 1/sky 0160 with Pat Clarke


  • Registered Users Posts: 6,235 ✭✭✭Oneiric 3


    24mm here since 18.00 ( gone light atm ) Going to be some totals by sat morning.

    Wind picking up avg 23 kph SSE, gust 45.1 kph

    Mild at 15C

    Not a drop yet here in Gallyway.

    New Moon



  • Registered Users Posts: 767 ✭✭✭davidsr20


    Dry as a bone here in Craughwell Galway.


  • Registered Users Posts: 6,827 ✭✭✭pauldry


    just went out to fix me rain gauge.

    wasnt working due to spiders web...those critters are about to drown!

    Id say we could see near 60mm here in Sligo

    Dont know if wel beat that 78mm

    That year the Geevagh road was closed to traffic as the water covered a lot of the land surrounding and just burst over the road

    Also Ballyfarnon remember the water being halfway up peoples walls.

    As its been dry for past 10 days there should be room for a bit before flooding hits


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  • Registered Users Posts: 15,286 ✭✭✭✭Supercell


    Sat24 infrared loop is showing the clouds pretty much stationary over Wales, is all this going to occlude by the time it reaches the east coast then stall and pivot? Could be some very large totals here if it doesn't peter out first, must have a look at the fax charts.

    Have a weather station?, why not join the Ireland Weather Network - http://irelandweather.eu/



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